Microhollow cathode discharges

TLDR

Microhollow cathode discharges exhibit a non‑Maxwellian electron energy distribution with a pronounced high‑energy tail. By miniaturizing hollow cathodes to the hundred‑micrometer scale, stable DC high‑pressure glow discharges are produced, and the resulting high electron energy and gas density enable efficient excimer generation, while abnormal‑glow operation permits microdischarge arrays without individual ballast. Measured excimer efficiencies range from 1 % to 9 % (up to 2 W cm⁻² for xenon), with 1 % VUV emission at 130.5 nm from Ar/O₂ mixtures and >20 % efficiency at 15 W cm⁻² when xenon discharges are pulsed, enabling excimer lamps and plasma reactors.

Abstract

By reducing the dimensions of hollow cathodes into the hundred micrometer range, stable, direct current, high (atmospheric) pressure glow discharges in rare gases, rare gas–halide mixtures and in air could be generated. The electron energy distribution in these microdischarges is non-Maxwellian, with a pronounced high-energy tail. The high electron energy together with the high gas density, which favors three-body collisions, is the reason for an efficient excimer generation in these microplasmas. Excimer efficiencies from 1% to 9% have been measured for argon, xenon, argon fluoride, and xenon chloride direct current excimer emitters, with a radiant excimer emittance of up to 2 W/cm2 for xenon. Adding small amounts of oxygen to argon has allowed us to generate vacuum ultraviolet line radiation at 130.5 nm with an efficiency approaching 1%. Pulsing xenon discharges with nanosecond electrical pulses has led to an increase in intensity to 15 W/cm2 and to a simultaneous increase in efficiency to more than 20%. Operating the discharges in an abnormal glow mode has allowed us to generate microdischarge arrays without individual ballast. Applications of these plasma arrays are excimer lamps and plasma reactors.